Pure, 24-karat gold does not rust, tarnish, or corrode under normal conditions because it is an extremely inert metal. However, “fake gold,” or imitation gold, is made by combining gold with other base metals or by coating a non-gold base metal with a thin layer of gold. These non-gold materials are chemically reactive and will degrade over time. This degradation is often mistakenly called rusting but is chemically known as tarnishing. Understanding the difference between these two chemical reactions explains why imitation gold eventually loses its luster.
The Difference Between Rust and Tarnish
Rust and tarnish are both forms of corrosion, but they involve distinct chemical processes and affect different metals. Rust is a specific term referring exclusively to the oxidation of iron or iron-based alloys, such as steel. This reaction occurs when iron interacts with oxygen and moisture, forming a reddish-brown substance called iron oxide. Unlike tarnish, rust continuously eats away at the metal, causing extensive damage.
Tarnish affects metals like silver, copper, and brass. This degradation is a surface-level reaction where the base metal reacts with nonmetal compounds, primarily sulfur compounds or oxygen. The resulting film is typically a metal sulfide or oxide that appears as a dull, gray, black, or greenish discoloration. Tarnish is generally self-limiting, as the thin surface layer often protects the underlying metal from further reaction.
Gold is classified as a noble metal because its electron structure makes it highly resistant to chemical reactions. This resistance is why 24-karat gold remains shiny and strongly resists losing electrons, the necessary step for corrosion. When gold is used in jewelry, it is alloyed with more reactive base metals like copper and silver to increase durability. These alloying metals are the components susceptible to tarnish.
How Different Types of Imitation Gold Degrade
The way imitation gold degrades depends on the physical structure and composition of the piece. Gold plating involves a microscopic layer of gold, often between 0.5 and 2.5 microns thick, applied to a base metal, typically copper or brass. This thin gold layer wears away quickly, especially on high-friction areas. Once the gold is breached, the exposed base metal reacts rapidly with air or moisture, causing discoloration.
When the plating fails, corrosion products from the base metal, such as copper oxide, can expand. This expansion creates pressure underneath the remaining gold layer, causing it to lift and separate in a process called undercutting. This degradation is often characterized by the base metal turning the skin green due to the formation of copper salts.
Gold-filled items offer a much thicker layer of gold than plating, as they must contain at least five percent gold by weight. This substantial gold layer provides better protection against the environment and wear. However, the base metal core, usually brass, will still be exposed if the piece is subjected to heavy friction or deep scratches, leading to localized tarnishing.
Even solid gold pieces with a lower purity, such as 10-karat or 14-karat gold, are susceptible to tarnishing. They contain a higher percentage of reactive base metals; 10-karat gold is only about 41.7% pure gold. These base metals react with sulfur compounds to form metal sulfides, which appear as a dull film on the surface. Rose gold, which contains a higher proportion of copper, is prone to tarnishing because copper is highly reactive.
Extending the Life of Imitation Gold Jewelry
Protecting imitation gold jewelry involves minimizing exposure to agents that accelerate tarnishing. Chemicals found in cosmetics, lotions, perfumes, and hairspray react with the base metals, so jewelry should always be the last item put on and the first taken off. Chlorine, found in swimming pools and hot tubs, is aggressive and causes rapid corrosion of the underlying metal.
Proper storage is an effective way to slow degradation by limiting exposure to air and moisture. Store each piece separately in a cool, dry place, ideally in an airtight bag or container, to reduce contact with oxygen and humidity. Including a small silica gel packet or anti-tarnish strip can help absorb ambient moisture and sulfur-containing gases.
Routine gentle cleaning removes the oils, dirt, and sweat that accumulate and speed up chemical reactions. After wearing a piece, wipe it down with a soft, lint-free cloth to remove surface contaminants. For a deeper clean, briefly soak the item in warm water mixed with mild dish soap, followed by a thorough rinse and complete drying. Abrasive materials or harsh cleaners must be avoided, as they quickly strip away the thin gold layer on plated items.